Liquid crystal display devices, which are thin, light-weight, and have low-power consumption, are used in a wide variety of applications such as monitors, projectors, portable phones, and portable digital assistant (PDA). As the types of the liquid crystal display devices, the transmissive type, the reflective type, and the semi-transmissive type (which performs both reflective and transmissive displays) have been known. In the transmissive type liquid crystal display devices, the light from the internal light source, such as a backlight, which is located behind the liquid crystal display panel, is guided from behind into the liquid crystal display panel, and then to the outside of the panel to display images. In reflective type liquid crystal display devices, external light or light from a front light source is guided to an interior of the liquid crystal display panel from the front (the viewer's side) and is reflected there to display images. The semi-transmissive type liquid crystal display devices primarily perform a transmissive display utilizing the light from the backside, and in addition, perform a reflective display utilizing light from the front when placed in an environment with high ambient light intensity, such as outdoors. Thus, the display characteristics of semi-transmissive type liquid crystal display devices, which have display properties of both the transmissive liquid crystal display device and the reflective liquid crystal display device, are less likely to be influenced by the external light conditions, and therefore superior display characteristics can be maintained in a wide range of environments.
In these semi-transmissive type liquid crystal display devices, the number of times the light passes through the liquid crystal layer is different between the transmissive display and the reflective display. Therefore, when the cell thicknesses of the transmissive region and the reflective region are set to be about the same, the effective retardations of the transmissive region and the reflective region are different. Thus, the gamma characteristics of the transmissive display and the gamma characteristics of reflective display do not match, causing a reversal of the gamma characteristics of the reflective display, which results in abnormal image display. In order to maintain good visibility for both the transmissive and reflective displays, a multi-gap structure in which the cell thickness in the reflective region is made about a ½ of the cell thickness in the transmissive region is generally known.
On the other hand, multi-domain vertical alignment liquid crystal display devices (hereinafter “MVA-LCDs”) in which liquid crystal with a negative dielectric constant anisotropy is vertically aligned and in which banks (linear protrusions) and electrode openings (slits) are provided on a substrate as orientation control means have been known.
In MVA-LCDs, the orientation of liquid crystal is controlled by slit openings formed in the electrodes and/or dielectric protrusions formed over the electrodes. When MVA-LCDs are used as semi-transmissive display devices, the area of the openings in the electrode and/or the surface area occupied by the protrusions on the substrate in the reflective region are made larger than the area of the openings in the electrode and/or the surface area occupied by the protrusions on the substrate in the transmissive region. This way, less voltage is applied to the liquid crystal layer in the reflective region than in the transmissive region, and consequently, the electrooptical properties of the reflective display can be matched to the electrooptical properties of the transmissive display (see, e.g., Patent Document 1).
In MVA-LCDs, however, the openings and protrusions employed as means to control the alignment cause a lowered aperture ratio. Low aperture ratio result in a low white luminance and darker image. This means that for MVA-LCDs, it is difficult to achieve high definitions, which require smaller pixel sizes. In this respect, the technology needs to be improved.
A technique for controlling the orientation of liquid crystal by means other than the openings and the protrusions are also known. This technique provides pretilt angles to liquid crystals using polymers (e.g., see Patent Document 2). In the technique where polymers are used for providing a pretilt angle to the liquid crystal, polymerizable components such as monomers and oligomers are mixed in the liquid crystal material, and the mixture is sealed between two substrates. The polymerizable components are polymerized while a voltage is applied across the substrates to keep the liquid crystal molecules tilted. This technique provides a liquid crystal layer having the liquid crystal molecules which are tilted to a predetermined direction upon voltage application. It should be noted that FIG. 4 of Patent Document 2 discloses a liquid crystal display device using a striped electrode having 3 μm-wide electrodes and a 3 μm-wide spaces.